The invention relates to apparatus for directly measuring the quantity .sqroot..rho. ck of a test specimen where .rho. is the density, c is the specific heat and k is the thermal conductivity of the specimen.
A previous technique for measuring the quantity .sqroot..rho. ck is disclosed in the U.S. Pat. No. 3,789,654. This previous technique consists of using a model made from a low thermal conductivity material covered with a phase-change coating which is an accurate surface temperature indicator. This indicator called "Tempilaq" consists of wax crystals which melt at a prescribed melting temperature. If the model is heated, the coating will melt when the surface reaches a calibrated phase-change temperature. Knowing this melt temperature, the time to reach the melt temperature from the initial temperature, and the heating rate, the combination of thermophysical properties .sqroot..rho. ck is determined from the equation: ##EQU2## WHERE Q is the imposed heating rate, T.sub.i is the initial model temperature prior to heating, T is the melting temperature and t is the elapsed time from the onset of heating until melting occurs.
In this prior technique a camera was used to record the sample surface temperature as indicated by the melting of the phase-change coating. Some of the disadvantages of this technique are that the camera may not photograph the sample at the exact time the phase-change coating melts; the exact time of phase transition is often difficult to interpret visually; the sample and calorimeter must be taken out of the apparatus in order to be coated with the phase-change coating; and the results may not be known for several days because of delays in photoprocessing and strip chart reading.
It is the primary purpose of this invention to provide apparatus for directly measuring the quantity .sqroot..rho. ck of a test specimen that eliminates disadvantages encountered in the measuring technique disclosed in U.S. Pat. No. 2,789,654.